a ring buffer

RingBuffer.scala

case class RingBuffer[A: ClassManifest](capacity: Int) extends IndexedSeq[A] {
  private val buffer = Array.fill[A](capacity)(null.asInstanceOf[A])
  private var _length = 0
  private var pos = 0
  def length = _length

  private def zero = (capacity + (pos - _length)) % capacity

  def clear() {
    _length = 0
    pos = 0
  }
  def +=(a: A) {
    buffer(pos % capacity) = a
    _length = math.min(_length + 1, capacity)
    pos += 1
  }

  def apply(i: Int) = buffer((zero + i) % capacity)
  def copy(capacity: Int = capacity) = {
    val b = RingBuffer[A](capacity)
    foreach { item => b += item }
    b
  }
}